Obstructive lung disease, including emphysema, chronic bronchitis, asthma and others, may lead to various obstructions and/or narrowing of airways within the bronchial tree. Airways that are affected by obstructive lung disease may include, for example, any of the trachea, main bronchi, lobar bronchi, segmental bronchi, sub-segmental bronchi, bronchioles, conducting bronchioles, terminal bronchioles and respiratory bronchioles. Airway obstructions may include the formation of mucous in the airways and/or scaring of the airways. Airway narrowing may be characterized by loss of radial tension of airways, thickening of the airway wall, and/or bronchoconstriction, among other examples. Further, obstructive lung disease may lead to breakdown of alveolar walls.
It becomes increasingly difficult for a patient to exhale as the airways or alveoli become damaged. Patients afflicted by obstructive lung disease may also face loss in muscle strength and an inability to perform common daily activities, among other ill effects. More detailed aspects of obstructive lung disease including additional aspects of the lungs, the bronchial tree, and airways are discussed further below.
There have been many attempts to cure and/or improve damage of the bronchial tree caused by obstructive lung disease. Other attempts have been made to relieve the obstruction and/or narrowing caused by obstructive lung disease. Still other attempts have been made to improve airflow into and out of the alveoli of a lung. However, these attempts have so far been met by many challenges.
Some treatments involve placement of a prosthetic, such as a conventional stent, in the central airways (i.e., the trachea, main bronchi, lobar bronchi, and/or segmental bronchi) in an attempt to maintain patency of these airways. Unfortunately, the central airways only contribute a portion of the overall airway obstruction and/or airway narrowing seen in patients with obstructive lung disease. Further, prosthetics, when placed in the bronchial airways, are plagued by issues of occlusion including the formation of granulation tissue and mucous impaction. Accordingly, treatments that involve the placement of conventional stents in airways often result in only short term improved outcomes for patients because the stent is eventually occluded.
Other treatments involve attempts to bypass an obstructed bronchial airway by forming a perforation through the chest wall into the outer portions of the lung, thereby creating a direct communication (i.e., bypass tracts) between diseased alveoli and outside of the body. If no other steps are taken, these bypass tracts will close by normal healing or by the formation of granulation tissue. Treating physicians may attempt to extend the duration of patency by placing a tubular hollow prosthetic in the bypass tract. However, such prosthetics can induce a foreign body reaction and accelerate the formation of granulation tissue, thereby causing the bypass tracts to eventually become occluded. Moreover, such a bypass procedure is difficult to perform, is time intensive, and is uncomfortable, inconvenient, and debilitating for the patient.
Yet other treatments involve forming a perforation between select central airways such as the main bronchi or lobar bronchi and the diseased alveoli in an attempt to bypass the obstructed connecting airways. If no other steps are taken, the perforations regularly heal closed, minimizing the long-term effectiveness of such treatments. Attempts have been made to maintain patency of the perforation by placing supporting stents in the lumen of the perforation. Additionally, the stents may be covered with silicone and/or coated with antiproliferative drugs to minimize the effect of the normal healing response and/or the foreign body reaction including granulation tissue formation. Unfortunately, however, these measures are typically inadequate and the supporting stents again induce a foreign body reaction including granulation tissue formation that often occludes the stent and results in closure of the perforation. Additionally, mucous produced from glands in the central airways often occludes the stent and results in closure of the perforation.
These and other problems continue to plague existing treatments for obstructive lung disease, and no reliable way to avoid such problems has yet been developed. It would therefore be desirable to develop treatments for issues caused by obstructive lung disease—including as examples obstruction and narrowing of airways of the bronchial tree—that more reliably avoid the problems encountered by existing treatments.